Oh, my understanding is that there is an ipad app for HBO Go, but that the app is not compatible with Airplay so there really isn't any way to get HBO Go onto the apple TV.

Sorry, I have a Mac Mini hooked to the same TV that I have my Apple TV hooked to. I thought I had watched HBO Go thru the iPad Airplay combination, but apparently I watched it thru the Mini....My apologies for the misinformation.

I still wonder if you will not be able to stream HBO Go from your Mac via Apple TVonce Mountain Lion is installed.